Effect of salinity stress on carbon assimilation, biochemical composition, and bioenergy potential of the microalga Coelastrella sp. KNUA068

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Microalgae, photosynthetic organisms that fix carbon dioxide, exhibit rapid growth and are considered promising as next-generation energy sources. The production of various intracellular biochemical products and bioactive compounds in microalgae increases under diverse stress conditions. However, exposure to concentrations beyond a certain level can act toxically, hindering overall microalgae productivity. This study explored the effects of varying concentrations of MgCl2 (75, 150 mM) and NH4Cl (8, 16 mM) on the indigenous microalgal strain Coelastrella sp. KNUA068 over 14 days. The findings indicate that higher concentrations of these chemicals reduced microalgae growth and diminished chlorophyll and carotenoid levels, except for the group treated with 8 mM NH4Cl, which showed an increase in these pigments. This suggests that moderate NH4Cl concentration acts as a beneficial nitrogen source rather than just a stressor. Biomass analysis revealed enhanced calorific value, lipid content, and protein content in NH4Cl-treated groups, unlike the MgCl2 groups, where only cetane numbers were higher. Additionally, biogas production from microalgal biomass was more productive compared to the control, indicating that specific stress conditions can improve biochemical compound productivity in Coelastrella sp. KNUA068, making it a promising bioenergy feedstock.